Various arrangements are known in which a control for an automatic kettle, for example, includes an element protector unit (such as the aforementioned Otter Control Z30) designed to switch off the supply of power to the element in the case of over-heating caused most commonly by switching on the kettle when empty, and also includes an automatic switch-off-on-boil unit (such as the aforementioned Otter Controls Z40) commonly responsive to generation of steam in the kettle. One such arrangement, which additionally is provided with a latching function requiring manual resetting in the case either of operation of the element protector or of the switch-off-on-boil unit, is described in British Patent Specification Nos. 1 470 365, 1 470 366 and 1 470 367, and this arrangement, known as the Otter Controls VEB and obtainable from Otter Controls Limited, has found widespread acceptance and approval. Another aspect of the present invention resides in the appreciation of the usefulness of such a latching member as above described in the construction of a latching element-protection and automatic switch-off-on-boil unit in which, for example, the two switch actuators of the unit, i.e., the actuator responsive to a dry switch-on or over-heating condition and the actuator responsive to boiling of the contents of the vessel in question, are arranged to operate a moving contact carrying leaf spring which has associated with it a latching member of the kind in question. As will be appreciated from descriptions given hereinafter of an exemplary unit, such use of a single latching element provides a simple and reliable mechanism.
The latching element can of course be used to perform separate latching functions in individual element protection (dry switch on) and automatic switch-off units and, in accordance with another advantageous aspect of the present invention, this gives rise to the possibility of a modular approach in which each of the element protection and automatic switch-off functions is performed separately by means of separate switch modules of the same basic configuration but with differently set temperature responses. Each module might for example comprise a temperature sensitive bimetallic switch actuator arranged to operate the moving contact of a switch contact pair and with a latching member of the kind described associated with the moving contact or with the bimetallic actuator. All such modules might be identically constructed, but with different bimetals set or operating at the respective different temperatures required, with consequent manufacturing advantages. Using this approach, two modules could be combined on one chassis so as to provide element protection and automatic switch-off facilities in the one unit, or alternatively the two modules could be separately associated with the vessel so as best to suit its particular configuration. The modules could have provision for the connection of neon indicator lamps or like indicating devices to the modules, or could even incorporate such devices, for providing an indication of the respective switch condition.
Yet a further aspect of the present invention is in regard to the subject matter of applicants' British Patent Application No. 8307104, filed Mar. 15, 1983 which concerns an element (dry switch-on) protector unit incorporating two independent thermal sensors, such as snap-acting bimetallic elements, each controlling a separate pair of switching contacts and each in intimate thermal contact with the head of the element. Such a system has been proposed, particularly for use with water boiling vessels formed of synthetic plastic material, to provide a back-up protection operative in the event (however unlikely) of the primary protector failing to operate. In further accordance with the present invention, a latching member of the general type aforementioned might be associated with each of the primary and secondary element protection switch units, either in the form of a separate latching member for each element protection switch or in a combined form wherein, in effect, two latching members are combined into a single integral unit. As in the previously mentioned modular approach, a neon or like indicator could be associated with the unit for example to indicate malfunction of the primary protector due to its contacts failing to open. If the neon were connected across the secondary contacts, the only time it would illuminate would be when the secondary contacts opened while the primary contacts were still closed, a condition which, as explained in British Patent Application No. 8307104, would not occur if the control were operating properly.
While the latching member may conveniently be formed, for example, as a moulding of a suitable synthetic plastic material, for some applications where it may be required to withstand many thousands of cyclical operations it may be preferable, for example, to construct the latching member as a plastics and metal composite with the resilient portion formed of metal.